1. Technical Field
This invention relates to a programmable shutter, and more particularly to a programmable shutter wherein a set of shutter blades are opened and closed by means of a stepping motor.
2. Prior Art
A programmable shutter wherein a shutter blade is opened and closed by means of a stepping motor is constructed such that driving pulses of a predetermined fixed period are inputted to a stepping motor in response to operation of a release mechanism to rotate the motor in a forward direction to gradually open a shutter sector, and at the time when the shutter sector is pivoted stepwise corresponding to an exposure quantity, the phase of the pulses is reversed to rotate the stepping motor in a reverse direction to close the shutter sector thereby to attain an appropriate exposure.
In general, since the maximum rotational speed of a stepping motor used for such a shutter is so low on the order of 500 to 1000 pulses per second or so, there are disadvantages that there is a restriction to a minimum time required for each incremental stepwise rotation, and a large error may be caused in the exposure, particularly in the case of short exposure time, or the optimum exposing steps may not be attained. Moreover, due to the advances being made in films of the present days, these have become significant problems.
While such problems can naturally be eliminated by reducing an inclination of an opening line of the shutter or by using a stepping motor which has a high rotational speed, or in other words, has a smaller stepping distance, such solutions will cause other new problems such as complicating the construction of the sector mechanism increasing the cost of the stepping motor.